27,443 research outputs found
A Realistic Particle Physics Dark Energy Model
We present a realistic dark energy model derived from particle physics. Our
model has essentially no free parameters and has an equivalent fit to the
observational data (CMB, SN1a and LSS) as LCDM and a better fit than the best
effective model. With the lack of a clear determination of the
cosmological parameters theoretical considerations should be taken seriously to
distinguish between dark energy models.Comment: 5 pages, RevTex, 6 figure
Domain walls and chaos in the disordered SOS model
Domain walls, optimal droplets and disorder chaos at zero temperature are
studied numerically for the solid-on-solid model on a random substrate. It is
shown that the ensemble of random curves represented by the domain walls obeys
Schramm's left passage formula with kappa=4 whereas their fractal dimension is
d_s=1.25, and therefore is NOT described by "Stochastic-Loewner-Evolution"
(SLE). Optimal droplets with a lateral size between L and 2L have the same
fractal dimension as domain walls but an energy that saturates at a value of
order O(1) for L->infinity such that arbitrarily large excitations exist which
cost only a small amount of energy. Finally it is demonstrated that the
sensitivity of the ground state to small changes of order delta in the disorder
is subtle: beyond a cross-over length scale L_delta ~ 1/delta the correlations
of the perturbed ground state with the unperturbed ground state, rescaled by
the roughness, are suppressed and approach zero logarithmically.Comment: 23 pages, 11 figure
On -dimensional supermanifolds
We define a -dimensional supermanifold as a manifold having q
odd coordinates and k + l even coordinates with l of them taking only nilpotent
values. We show that this notion can be used to formulate superconformal field
theories with different number of supersymmetries in holomorphic and
antiholomorphic sectors.Comment: 19 pages, Late
Topological aspects in non-Abelian gauge theory
We discuss the BRST cohomology and exhibit a connection between the Hodge
decomposition theorem and the topological properties of a two dimensional free
non-Abelian gauge theory having no interaction with matter fields. The
topological nature of this theory is encoded in the vanishing of the Laplacian
operator when equations of motion are exploited. We obtain two sets of
topological invariants with respect to BRST and co-BRST charges on the two
dimensional manifold and show that the Lagrangian density of the theory can be
expressed as the sum of terms that are BRST- and co-BRST invariants.Comment: (1+11) pages, LaTeX, no figure
The essence of quintessence and the cost of compression
Standard two-parameter compressions of the infinite dimensional dark energy
model space show crippling limitations even with current SN-Ia data. Firstly
they cannot cope with rapid evolution - the best-fit to the latest SN-Ia data
shows late and very rapid evolution to w_0 = -2.85. However all of the standard
parametrisations (incorrectly) claim that this best-fit is ruled out at more
than 2-sigma, primarily because they track it well only at very low redshifts,
z < 0.2. Further they incorrectly rule out the observationally acceptable
region w 1. Secondly the parametrisations give wildly different
estimates for the redshift of acceleration, which vary from z_{acc}=0.14 to
z_{acc}=0.59. Although these failings are largely cured by including
higher-order terms (3 or 4 parameters) this results in new degeneracies which
open up large regions of previously ruled-out parameter space. Finally we test
the parametrisations against a suite of theoretical quintessence models. The
widely used linear expansion in z is generally the worst, with errors of up to
10% at z=1 and 20% at z > 2. All of this casts serious doubt on the usefulness
of the standard two-parameter compressions in the coming era of high-precision
dark energy cosmology and emphasises the need for decorrelated compressions
with at least three parameters.Comment: 7 pages, 4 colour figures, EmulateApJ; v2: includes Bayesian evidence
analysis and table that were only present in published version, because of
increased interest in Bayesian model comparison (no new material beyond the
one in the published ApJL of 2004
The hepta-β-glucoside elicitor-binding proteins from legumes represent a putative receptor family
The ability of legumes to recognize and respond to β-glucan elicitors by synthesizing phytoalexins is consistent with the existence of a membrane-bound β-glucan-binding site. Related proteins of approximately 75 kDa and the corresponding mRNAs were detected in various species of legumes which respond to beta-glucans. The cDNAs for the beta-glucan-binding proteins of bean and soybean were cloned. The deduced 75-kDa proteins are predominantly hydrophilic and constitute a unique class of glucan-binding proteins with no currently recognizable functional domains. Heterologous expression of the soybean beta-glucan-binding protein in tomato cells resulted in the generation of a high-affinity binding site for the elicitor-active hepta-β-glucoside conjugate (K-d = 4.5 nM). Ligand competition experiments with the recombinant binding sites demonstrated similar ligand specificities when compared with soybean. In both soybean and transgenic tomato, membrane-bound, active forms of the glucan-binding proteins coexist with immunologically detectable, soluble but inactive forms of the proteins. Reconstitution of a soluble protein fraction into lipid vesicles regained beta-glucoside-binding activity but with lower affinity (K-d = 130 nM). We conclude that the beta-glucan elicitor receptors of legumes are composed of the 75 kDa glucan-binding proteins as the critical components for ligand-recognition, and of an as yet unknown membrane anchor constituting the plasma membrane-associated receptor complex
The Loss Rank Principle for Model Selection
We introduce a new principle for model selection in regression and
classification. Many regression models are controlled by some smoothness or
flexibility or complexity parameter c, e.g. the number of neighbors to be
averaged over in k nearest neighbor (kNN) regression or the polynomial degree
in regression with polynomials. Let f_D^c be the (best) regressor of complexity
c on data D. A more flexible regressor can fit more data D' well than a more
rigid one. If something (here small loss) is easy to achieve it's typically
worth less. We define the loss rank of f_D^c as the number of other
(fictitious) data D' that are fitted better by f_D'^c than D is fitted by
f_D^c. We suggest selecting the model complexity c that has minimal loss rank
(LoRP). Unlike most penalized maximum likelihood variants (AIC,BIC,MDL), LoRP
only depends on the regression function and loss function. It works without a
stochastic noise model, and is directly applicable to any non-parametric
regressor, like kNN. In this paper we formalize, discuss, and motivate LoRP,
study it for specific regression problems, in particular linear ones, and
compare it to other model selection schemes.Comment: 16 page
Two Component Model of Dark Energy
We consider the possibility that the dark energy is made up of two or more
independent components, each having a different equation of state. We fit the
model with supernova and gamma-ray burst (GRB) data from resent observations,
and use the Markov Chain Monte Carlo (MCMC) technique to estimate the allowed
parameter regions. We also use various model selection criteria to compare the
two component model with the LCDM, one component dark energy model with static
or variable w(XCDM), and with other multi-component models. We find that the
two component models can give reasonably good fit to the current data. For some
data sets, and depending somewhat on the model selection criteria, the two
component model can give better fit to the data than XCDM with static w and
XCDM with variable w parameterized by w = w_0 + w_az/(1+z).Comment: 10 pages, 8 figures, 3 tables; Version accepted by PR
Black Hole Entropy, Topological Entropy and the Baum-Connes Conjecture in K-Theory
We shall try to exhibit a relation between black hole entropy and topological
entropy using the famous Baum-Connes conjecture for foliated manifolds which
are particular examples of noncommutative spaces. Our argument is qualitative
and it is based on the microscopic origin of the Beckenstein-Hawking
area-entropy formula for black holes, provided by superstring theory, in the
more general noncommutative geometric context of M-Theory following the Connes-
Douglas-Schwarz article.Comment: 17 pages, Latex, contains an important paragraph in section 2 which
gives a better understandin
- …